1. Field of the Invention
This invention relates to an independent wheel suspension apparatus for use mainly in the front wheels of an automobile and more particularly to a wishbone type independent suspension apparatus.
2. Description of the Prior Art
For an automobile in motion to absorb various vibrations and shocks inflicted thereon by the road surface, a suspension endowed with a shock-absorbing ability is interposed between the body and the axles of the automobile. The suspension of this nature fulfills such important roles as supporting the automobile on the road surface, transmitting the propelling force from the driving wheels to the automobile side, simultaneously moderating the shocks from the road surface and protecting the automobile against breakage, and improving the ride and the stability of motion as well. The trend of automobiles toward the improvement of speed has been urging increasingly profound recognition of the performance of the suspension as a factor for governing the limit of speed improvement. Scientific studies have been being promoted concerning the suspension system as a whole, achieving success in developing a host of types of mechanisms and elements.
The suspension generally needs to produce soft motions in the vertical directions and hard motions in the longitudinal and lateral directions. In terms of construction, the suspensions may be classified broadly under the two types, axle suspensions and independent suspensions. While the axle suspensions are generally used in the front and rear wheels of trucks and in the rear wheels of passenger cars, the independent suspensions are prevalently used in the front and rear wheels of passenger cars which attach great importance to comfort of the ride and stability of the motion.
The independent suspensions allow the laterally opposite wheels to produce motions independently of each other instead of interconnecting them with one axle. In terms of construction, these independent suspensions may be classified under the wishbone type, the McPherson type, the trailing arm type, and the swing axle type. These independent suspensions, as compared with the axle suspensions, have the advantage that when either of the laterally opposite wheels rides on a projection from the road surface, they act like human knee joints, allow only the affected wheel to produce a vertical motion, keep the automobile body from inclination, curb the possible rolling, and ensure stability of the automobile motion.
Among other independent suspensions cited above, the wishbone type suspension has found veritably popular utility. This wishbone type suspension is characterized in that since a link mechanism using two horizontally parallel separate arms produces parallelogrammatic motions, the wheels produce substantially vertical motions and, as a result, the tires on the wheels always keep a horizontal contact with the road surface and enjoy ideal ground contact. It nevertheless has many problems such as heavy weight and high cost due to the complication of construction as compared with the McPherson type suspension and reduction in inner volume of the engine room due to the inevitable intrusion of the two arms into the engine room. It has come to attract growing attention on account of the merits of robustness of build and excellent stability in rotary motion.
The wishbone type independent suspension is provided with two separated horizontal arms resembling a furcula of the breastbone in a chicken (wishbone) and has knuckles thereof attached by these arms to the automobile body or the frame thereof. The basal terminals severally of these arms are pivotally supported on the automobile body side and the leading terminals thereof are connected to the upper and lower terminals of the knuckles generally through the medium of a ball joint. As a result, the two separated horizontal arms and the knuckles jointly form a link mechanism. In addition to the wishbone type suspension which has both the two arms formed in the shape of the letter A, a modified version which has a lower arm not formed in the shape of the letter A but adapted to rely on a tension rod for compensation of the motion thereof produced in the longitudinal directions has been known to the art. This modified type is referred to as the I type arm.
In the wishbone type independent suspension disclosed in Japanese Unexamined Utility Model Publication No. 62-189,211, for example, the socket of a ball joint serving to interconnect an upper arm and a knuckle is rotatably attached to the leading terminal of the upper arm through the medium of a pivot shaft. Then, on the leading terminal of a boss part protruding upwardly from this socket, a sub-upper arm is supported by means of a pivot shaft. Owing to this construction, the suspension is enabled by the upper arm to follow the vertical strockes of the wheel.
This suspension, while enjoying improved characteristic of change in camber angle due to the vertical motions of the wheel and enhanced stability of a straight motion, requires to decrease the angle of inclination of a kingpin and increase the angle of a castor for the purpose of conferring an angle of negative camber on the outer wheel during a rotation of the vehicle thereby satisfactorily improving the stability of a rotary motion. A reduction in the angle of inclination of the kingpin results in an addition to the radius of scrub and an increase in the angle of castor results in an excessive addition to the castor trail. These disadvantages have prevented the suspension from acquiring generous negative camber.